Author

Creative Commons License

Date of Award

Summer 2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Department of Biology

Abstract

As female participation in athletics has increased, it has become apparent that sex differences exist in sports-related injury types and frequencies. The purpose of this study is to examine the effects of exercise and the sex hormone estradiol on sex differences in foot and ankle laxity and plantar pressure. We measured serum estradiol, pre- and post-fatigue ankle and toe laxity, and pre- and post-fatigue plantar pressure in 47 subjects (34 female, 13 male) once a week for 12 weeks. We compared laxity and plantar pressure in females not using oral contraceptive (NOC) to females using oral contraceptives (OC) and males. Relative estradiol level was regressed against plantar pressure variables and laxity pre- and post-exercise. The results of this study demonstrated that females had higher ankle and first metatarsophalangeal (MP1) joint laxity than males. There were no differences in ankle and MP1 laxity between OC and NOC groups or across the menstrual cycle. There was no relationship between estradiol levels and ankle/MP1 joint laxity. The exercise protocol caused an increase in MP1 joint laxity but did not alter ankle laxity. Despite no changes in speed, stride length, or step length, post-exercise peak pressure in the toes and metatarsals 1 and 2 regions decreased while peak pressure in the medial midfoot increased. Contact area increased in metatarsals 1 and 2 and toe 1 while maximum force remained the same. There was no relationship between peak plantar pressure and joint laxity in any foot regions or in either joint. Males had higher toe 1 peak pressures than females and metatarsal 1 and 2 peak pressures were higher in the NOC group compared to the OC group. Peak pressure was not different across the menstrual cycle for any foot region. Joint laxity is increased by repetitive loading from exercise and higher levels of estradiol in females than males. Influences in joint laxity are not evident at the lower levels of sex hormone involved in monthly fluctuation. Increased joint laxity may increase the risk for ligamentous injury which might explain why females have higher rates of ankle sprains compared to males, especially after exercise. Additionally, joint laxity and muscular fatigue in response to repetitive loading from exercise potentially increase bone strain and raise the risk for stress fractures by providing less support to the bone. The metatarsals 1 and 2 might be a common site for stress fractures because maximum force remains the same after the supporting muscles are fatigued and surrounding soft tissues are stretched out. Repetitive loading also increases medial midfoot pressure which raises the risk for shin splints and patellofemoral overuse injury. Prevention strategies will likely need in incorporate strength and endurance training as well as optimizing joint laxity.